The present disclosure is directed to an optical scanner for a differential light scattering analyzer for microparticles, and is particularly useful in the automated testing of the response of bacteria to therapeutic agents, such as antibiotics.
The principles of operation of a differential light scattering analyzer for microparticles are discussed in detail in U.S. Pat. No. 3,770,351 to Wyatt, issued Nov. 6, 1973 and U.S. Pat. No. 3,928,140 to Wyatt et al, issued Dec. 23, 1975, which patents are hereby incorporated by reference.
Briefly, a differential light scattering analyzer may be employed to rapidly analyze microparticles by measuring the light scattering properties of the particles. In the analyzer a collimated beam of electromagnetic radiation, such as from a laser, is directed at a test sample containing the particles. One or more detectors are employed to produce signals representing the scattered light intensity from the microparticles at different angles relative to the incident laser beam. Where the microparticles are bacteria, it has been observed that the differential light scattering properties provide indicia of the growth of the bacteria and/or its morphology.
The present invention relates to a scanner for scanning a small volume of microparticles at different radial angles. The disclosed scanner is well adapted for use in an automated differential light scattering analyzer, capable of quickly and accurately making differential light scattering measurements for a large number of test samples.
A differential light scattering analyzer, known in the prior art, is illustrated in the above-referenced U.S. Pat. No. 3,770,351 to Wyatt. Wyatt discloses directing a highly collimated incident beam of light at a test sample located at the center of a test chamber. A plurality of detectors are mounted about the test chamber at equal radial distances from the test sample. Scattered radiation is sensed by each of these light detectors, each detector sensing the light intensity at a different, fixed, observation angle with respect to the incident beam.
The system disclosed by Wyatt has the disadvantage in that it requires a detector to be located at each angular location about the test sample at which a scattering intensity measurement is to be made. Since the effectiveness of the analyzer is increased by making highly accurate intensity measurements at a large number of different radial angles (e.g. 100 different angles), to achieve this accuracy, the Wyatt system would require the use of a large number of detectors, calibrated with respect to one another.
Accordingly, it is an object of the present invention to provide a simply and inexpensively fabricated scanner for producing an accurate measurement of the intensity of scattered radiation from a microparticle test sample at a number of different scattering angles.
It is another object of the present invention to provide a simply and inexpensively fabricated radial scanner which employs a single photodetector.
Another differential light scattering analyzer known in the prior art is illustrated in the above-referenced U.S. Pat. No. 3,928,140 to Wyatt et al. In the Wyatt et al patent, an incident, collimated beam of light from a laser is directed at a stationary test sample containing microparticles. A detector periscope, comprising a number of optical elements, directs scattered light to a photomultiplier tube. The periscope is rotated through an arc about the test sample to produce signals at the photomultiplier representing the scattered light intensity as a function of the angle of scattering relative to the incident laser beam. The periscope is driven back and forth in an arc around the test sample through an angular range of from 30.degree. to 130.degree. with respect to the direction of the incident laser beam.
This Wyatt el al system has the disadvantage in that the sensitive periscope optics must be driven through the 100.degree. arc, then abruptly reversed in direction and driven backwards through the 100.degree. arc to perform a scan of the test sample. In order to provide rapid measurement in an automated high volume analyzer, the periscope would have to be driven at a high speed, thereby increasing the potential for misaligning of the optics. The drive mechanism for rotating the periscope must be manufactured to very high tolerances to prevent objectionable eccentricity in the arc through which the periscope moves and to prevent misalignment of the periscope with respect to the test sample during a portion of the arc. Moreover, the control system for the motor driving the periscope through the arc must be coordinated with the analyzer circuits so that the test is properly sequenced and so that intensity measurements are properly identified with the particular angular positions at which they are made.
Accordingly, it is an object of the present invention to provide an optical scanner for a differential scattering analyzer which is capable of accurately scanning a test sample from different radial angles at a high rate of speed.
It is another object of the present invention to provide a radial scanner for a differential light analyzer which employs a small number of moving optical elements.
It is another object of the present invention to provide a radial scanner for a differential light analyzer which minimizes the acceleration and deceleration of optical elements used therein.
It is yet another object of the present invention to provide a radial scanner for a differential light scattering analyzer which minimizes the distance of travel of the moving optical elements.
A number of scanners are known in the prior art which employ rotating planar mirrors to reflect light on a curved stationary mirror. Such scanners are shown for example in U.S. Pat. No. 3,469,030 to Priebe, U.S. Pat. No. 3,520,586 to Bousky and U.S. Pat. No. 4,029,389 to Runciman. However, such scanners are concerned with scanning a line or scanning a generally planar surface with a focused beam of light. Such systems are not adapted to scan a small volume or point from different radial angles and are not adapted for use in a detector of scattered light from a scanned volume. Since these systems cannot perform radial scanning, they cannot, of course, function to perform the radial scanning required for differential scattering analysis.
Accordingly, it is the object of the present invention to provide a radial scanner employing a single rotating mirror.